Hydraulic actuators may be held in place against an external load by a load holding valve in lieu of continuous operation of a hydraulic pump. Fluid in the circuit between the load holding valve and the hydraulic pump may become depressurized by leakage through the pump. Thereafter, when the load holding valve opens, the hydraulic actuator may jerk due to pressurized fluid between the load holding valve and the actuator rushing in to the depressurized zone between the valve and the pump.
US Patent Application Publication No. US20080295504 A1 (Method for controlling a hydraulic cylinder in a work machine) proposes a solution to this problem where the electrically driven hydraulic pump is driven in the “wrong direction” (i.e. in a direction that would normally cause extension of the actuator against the external load when the desired movement is actually in the opposite direction) when an operator command is given. The torque applied to pressurize the hydraulic line is based upon a pressure sensor reading taken immediately prior to starting the routine. A second alternative is proposed where the electrically driven hydraulic pump is driven in the “wrong direction” when an operator command is given, and the duration of pressurizing the hydraulic line is based upon a position sensor reading taken during the routine, with the routine being stopped when actuator motion is sensed to be in the “wrong direction”.